It has recently been shown that a soluble beta-galactoside specific lectin (Mac-2) is expressed on mouse blastocysts just prior to the time of embryo attachment to the uterine epithelium and that it accumulates in large amounts at the feto-maternal interface within developing implantation sites. Because Mac-2 has been associated with a variety of important functions including cell-recognition/adhesion and local immunomodulation in other cellular environments, its localization to the region of contact between the implanting conceptus and its mother led us to undertake experiments to establish the ontogeny of this lectin in the implantation site as well as to determine what role it plays in pregnancy. The spatio-temporal pattern of expression of Mac-2 in early implantation sites and deciduomata will be established by immunohistochemistry using the anti-Mac-2 monoclonal antibody (M3/38) on frozen sections of the mouse uterus at various stages of implantation and placental development. Because Mac-2 is a soluble extracellular protein that binds to the cell surface by means of its carbohydrate binding site, it will be important to compare the spatio-temporal pattern of expression of the protein with that for its mRNA. That will be done by means of in situ hybridization histochemistry using a labeled antisense mRNA probe on frozen sections of the uterus adjacent to those used to examine distribution of the protein. Additional studies will be undertaken to resolve the functional role of this soluble lectin in the processes of implantation and placentation. First, a monospecific function perturbing polyclonal antiserum against Mac-2 will be used to determine whether immunoneutralization of the lectin interferes with attachment and trophoblastic outgrowth in vitro or perturbs the processes of implantation or placentation in vivo. And second, the endogenous uterine ligands for Mac-2 will be isolated by means of immunoprecipitation (again with M3/38) and a monospecific function perturbing polyclonal antiserum will be prepared in a rabbit against the purified ligands(s). If that effort proves to be successful, the resulting antiserum will be used both for immunocytochemistry to establish the spatio-temporal pattern of expression of the Mac-2 ligand in the implantation site for comparison with that for the lectin and its mRNA, and for passive immunization of pregnant females in hopes of perturbing ligand function in situ during implantation and placentation.